1. Technical Field
The instant disclosure relates to a wireless communication technique, and in particular, to an antenna system and an antenna structure thereof.
2. Description of Related Art
With the prevalence of portable electronic devices (such as smart phones, tablets, notebooks), more and more attention is being drawn to wireless communication technology. The wireless communication quality of portable electronic devices depends on the antenna efficiency thereof. Therefore, how to increase the radiation efficiency of the antenna and how to more easily adjust the overall frequency has become an important issue in the art.
In addition, since the electromagnetic wave generated by the antenna is harmful to human body, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) recommends that the value of the Specific Absorption Rate (SAR), which is the ratio of the mass of a living body to the absorbed electromagnetic energy, be less than 2.0 W/Kg, and Federal Communication Commission (FCC) recommends that the SAR be less than 1.6 W/Kg. However, in order to improve the antenna efficiency, the products in the existing art have relatively high SAR values.
Recently, products combining laptop and tablet are developed, such as Hybrid laptops or 2-in-1 laptops. The laptops can be operated under a general mode or under a tablet mode. However, the existing antenna structure cannot meet the recommended SAR value under the tablet mode. U.S. Pat. No. 8,577,289 discloses an “Antenna with integrated proximity sensor for proximity-based radio-frequency power control” which adjusts the emission power of the antenna according to human body signals. However, since in the abovementioned patent, two grounding capacitors are disposed between the feeding terminal and the transceiver for providing the antenna the function of detection, the two capacitors will adversely affect the antenna performance and reduce the detection distance thereof.